Interlaced signals to be converted into progressive signals are classified into ordinary signals for images scanned by interlaced scanning and interlaced signals converted from progressive signals. A typical example of the latter is a telecine-converted signal.
In a 2-2 pulldown method, which is a telecine conversion method, the telecine-converted signal is generated as follows. Firstly, frames of a 24 frame-per-second movie film are sequentially scanned to generate a 24 frame-per-second progressive signal. Then, each frame (parent frame) of the progressive signal is converted into an odd field of an interlaced signal and an even field following immediately thereafter.
For example, the first frame of a movie film (a first parent frame of the progressive signal) is converted into first and second fields, while the second frame of the movie film (a second parent frame of the progressive signal) is converted into third and fourth fields.
Thus, visual images in the first and second fields converted from the same parent frame are similar to each other, and therefore there is only a small difference between the visual images. As for the second and third fields converted from different parent frames, an inter-field visual difference reflects a difference between the parent frames, and therefore is large as compared to the former case. That is, a difference between adjacent fields varies alternately between large and small among the fields in accordance with a parent frame-to-field relationship.
Such a characteristic of the telecine-converted signal also holds for a 60 field-per-second interlaced signal obtained by 2-2 pulldown-converting a progressive signal captured by a 30 P video camera for generating a 30 frame-per-second progressive video signal.
Also, in a 2-3 pulldown method which is used for telecine conversion to an NTSC (60 field-per-second) interlaced signal, one frame of the movie film is converted into two fields, and the next frame is converted into 3 fields, and the conversion pattern is repeated for every two frames. A 2-3 pulldown telecine-converted signal also has the above characteristic because it exhibits a regular pattern in which an inter-field pixel level difference varies in accordance with a parent frame-to-field relationship.
Japanese Laid-Open Patent Publication No. 9-18784 (claiming a priority of U.S. application No. 94-366799) discloses a field interpolation method determination device which identifies whether an input interlaced signal is a telecine-converted signal based on an inter-field difference of the input interlaced signal, and determines a field interpolation method.
Referring to FIG. 10, a video signal processing device having incorporated therein a conventional field interpolation method determination device is described. A video signal processing device 200 shown in the figure converts an interlaced signal into a progressive signal by carrying out inter-field interpolation only when an interlaced signal is a telecine-converted signal, while intra-field interpolation is carried out if it is not the telecine-converted signal.
The video signal processing device 200 includes an input terminal 1, a field memory 2, a field memory 4, a subtractor 6, a field interpolation method determination section 108, an ODD/EVEN detection section 10, a first switch 12, a line memory 14, a 2-line interpolation section 16, a second switch 18, and a progressive signal generation section 20.
The input terminal 1 is supplied with an input interlaced signal Vin. The field memory 2 outputs a 1-field delay input interlaced signal Vd1 delayed by one field with respect to the input interlaced signal Vin. The 1-field delay input interlaced signal Vd1 is inputted into the progressive signal generation section 20 where either inter-field interpolation or intra-field interpolation is performed on the signal.
The subtractor 6 obtains a difference in pixel level between the input interlaced signal Vin and the 1-field delay input interlaced signal Vd1, and outputs it as an inter-field pixel level difference Sp. Note that in the interlaced signal, scanning lines of adjacent fields are displaced by one row from each other. Accordingly, the subtractor 6 obtains a difference between an average pixel level for two adjacent lines in one field and a corresponding pixel level in the other field.
The field interpolation method determination section 108 determines whether the input interlaced signal Vin is a telecine-converted signal based on the inter-field pixel level difference Sp. The field interpolation method determination section 108 outputs a field interpolation method instruction signal Dvp that instructs to perform either the inter-field interpolation or the intra-field interpolation on the 1-field delay input interlaced signal Vd1.
If a field interpolation method instruction signal Dvp, which instructs to perform the inter-field interpolation is inputted, the second switch 18 selects an inter-field interpolation video signal Sw1 outputted from the first switch 12, and outputs it as an interpolation video signal Sw2.
The inter-field interpolation video signal Sw1 is either of a 2-field delay input interlaced signal Vd2 and an input interlaced signal Vin, which respectively correspond to fields before and after the 1-field delay input interlaced signal Vd1, and it is selected as follows.
The ODD/EVEN detection section 10 detects whether the signal corresponds to an odd field or an even field based on the 1-field delay input interlaced signal Vd1, and outputs a field identification signal Doe which indicates a detection result.
The first switch 12 selects either the 2-field delay input interlaced signal Vd2 or the input interlaced signal Vin based on the field identification signal Doe, and outputs it as the inter-field interpolation video signal Sw1. Specifically, the first switch 12 outputs the input interlaced signal Vin if the 1-field delay input interlaced signal Vd1 corresponds to an odd field, while it outputs the 2-field delay input interlaced signal Vd2 if the 1-field delay input interlaced signal Vd1 corresponds to an even field.
The progressive signal generation section 20 interpolates the 1-field delay input interlaced signal Vd1 with the interpolation video signal Sw2 outputted from the second switch 18 (in this case, either one of the current signal Vin and the 2-field delay input interlaced signal Vd2, which has been selected by the first switch 12), thereby generating a progressive signal. The frame of the thus-generated progressive signal is identical to the original parent frame, and enhanced in terms of vertical resolution as compared to a frame generated by intra-field interpolation which will be described later.
On the other hand, if a field interpolation method instruction signal Dvp, which instructs to carry out intra-field interpolation, is outputted from the field interpolation method determination section 108, the second switch 18 selects an intra-field interpolation video signal Vd1S outputted from the 2-line interpolation section 16, and outputs it as an interpolation video signal Sw2.
The 2-line interpolation section 16 generates an intra-field interpolation video signal Vd1S based on a 1-line delay signal Vd1L, which is obtained by delaying the 1-field delay input interlaced signal Vd1 by one line in the line memory 14, and the 1-field delay input interlaced signal Vd1.
The progressive signal generation section 20 interpolates the 1-field delay input interlaced signal Vd1 with the interpolation video signal Sw2 outputted from the second switch 18 (in this case, the intra-field interpolation signal Vd1S), thereby generating a progressive signal.
The subtractor 6 and the field interpolation method determination section 108 shown in FIG. 10 correspond to the conventional field interpolation method determination device. Referring to FIG. 11, the conventional field interpolation method determination device is described. FIG. 11 is a block diagram showing a detailed structure of the field interpolation method determination section 108 shown in FIG. 10.
The field interpolation method determination section 108 includes an absolute value circuit 81, a pixel difference determination comparator 82, a cumulative adder 83, an inter-field correlation determination comparator 84, a first register 85, a second register 86, a 2-field difference determination comparator 189, an exclusive-OR (EOR) circuit 190, a counter 92, and a count determination comparator 93.
Although not shown, a field pulse VP and a frame pulse FP are generated by a timing generation circuit.
The absolute value circuit 81 obtains an absolute value of the inter-field pixel level difference Sp, which is calculated by the subtractor 6 and corresponds to a difference in level between pixels of the input interlaced signal Vin and the 1-field delay input interlaced signal Vd1, and outputs an inter-field pixel level difference absolute value SpA.
The pixel difference determination comparator 82 compares the inter-field pixel level difference absolute value SpA with a predetermined first threshold X to provide a determination as to whether two comparison target fields have at least a great difference (a significant difference) in pixel level to such an extent that they are considered as being derived from the same parent frame. As an inter-field pixel difference determination signal Dp, which indicates a result of the determination, the pixel difference determination comparator 82 outputs “1” if the determination is “significant difference”, or outputs “0” if it is “no significant difference”.
The cumulative adder 83 outputs an inter-field pixel difference determination cumulative value CDp which is obtained by cumulatively summing inter-field pixel difference determination signals Dp. The inter-field pixel difference determination cumulative value CDp is a value which indicates the number of pixels having been determined as having a “significant difference” between fields of the input interlaced signal Vin and the 1-field delay input interlaced signal Vd1. Note that the cumulative adder 83 is reset for each field by the field pulse VP.
If the inter-field pixel difference determination cumulative value CDp is greater than a predetermined threshold Y, the inter-field correlation determination comparator 84 determines that there is a difference between the fields. Then, it outputs an inter-field correlation determination signal Df which indicates a result of the determination.
The value of the inter-field correlation determination signal Df is “1” if there is a difference, or outputs “0” if there is no difference.
The first register 85 and the second register 86 are D-flip-flops, and supplied with the field pulse VP as a clock. An inter-field determination result is supplied to a series circuit composed of the first register 85 and the second register 86. The first register 85 and the second register 86 output an inter-field difference stored therein to the 2-field difference determination comparator 189 and the EOR circuit 190, respectively.
In the case where outputs of the first register 85 and the second register 86 are respectively “0” and “1”, or “1” and “0”, differential relationships between two sequential fields in respective cases are “small and large”, and “large and small”. That is, they show the above-described characteristic of the telecine-converted interlaced signal. In such a case, the 2-field difference determination comparator 189 determines that the input interlaced signal Vin has been telecine-converted, and outputs “1” to increment the counter 92.
On the other hand, if the outputs of the first register 85 and the second register 86 are respectively “0” and “0”, or “1” and “1”, the differential relationships between the two sequential fields are “small and small” or “large and large”. That is, they do not show the above-described characteristic of the telecine-converted interlaced signal. In such a case, the EOR circuit 190 resets the counter 92.
As described above, the counter 92 is incremented or reset. If a count value CDs of the counter 92 reaches a predetermined value Z, the count determination comparator 93 outputs a field interpolation method instruction signal Dvp that instructs to perform inter-field interpolation on fields of the input interlaced signal.
In actuality, however, there are various types of visual images, and therefore in some cases, it is not possible to detect a difference between parent frames of even the telecine-converted signal as a difference between fields because there is no difference or only a slight difference between the parent frames. In such a case, the field interpolation method determination device is not able to detect the telecine-converted signal.
For example, in the case of video consisting of continuous still images, where images in two parent frames are identical to each other, a difference between fields converted from different parent frames is naturally small. In such a case, the field interpolation method determination device is not able to detect the difference between the parent frames based on the difference between fields. Consequently, the conventional field interpolation method determination device is not able to detect an inter-field variation pattern specific to the telecine-converted signal, and therefore the interlaced signal is determined not to be the telecine-converted signal.
Also, in visual images of dark scenes, even if they are dynamic images, there is only a small difference in pixel level between parent frames, and therefore a difference between fields converted from different frames is also small. In such a case, similar to the above case, the field interpolation method determination device determines that the interlaced signal is not the telecine-converted signal.
Also, for example, in the case where interlaced signals for commercials, etc., which have a different frame correlation, are inserted between interlaced signals for a program, correlations between parent frames and correlations between fields may vary in a specific manner. In such a case, an inter-field difference variation pattern specific to the telecine-converted signal varies in a specific manner, and therefore, similar to the above case, the field interpolation method determination device determines that the interlaced signals are not telecine-converted signals.
As such, in the case where a difference between at least two frames cannot be detected, the conventional field interpolation method determination device is not able to identify the telecine-converted signal, even if the input interlaced signal is the telecine-converted signal. As a result, the video signal processing device carries out intra-field interpolation until input interlaced signals for at least a predetermined number of fields are continuously determined to be the telecine-converted signal. Accordingly, it is often the case where an original parent frame cannot be generated with high vertical resolution.
Also, the above conventional technique has been described such that in the telecine conversion, a parent frame is generally converted into an odd field and an even field following immediately thereafter. In actuality, however, on rare occasion, a telecine-converted signal is obtained by converting the parent frame into an even field and an odd field following immediately thereafter.
The conventional field interpolation method determination device selects a frame immediately before or after an interpolation target signal as an interpolation video signal depending on whether the target signal corresponds to an odd frame or an even frame. Accordingly, in a signal where positional relationships between fields converted from parent frames are reversed, two fields converted from different parent frames are interpolated with each other and converted into one frame. As a result, different images are present in one frame, and therefore video quality of a progressive signal obtained by conversion is considerably deteriorated.
Therefore, an object of the present invention is to provide a field interpolation method determination device capable of accurately detecting a field-to-frame relationship of an input interlaced signal even if it is not possible, or it is difficult, to specifically detect a difference between parent frames, thereby determining whether to use either inter-field interpolation or intra-field interpolation to perform an interpolation operation.